EP0133112A1 - Method and apparatus for manufacturing transparent plastic films, sheets or ribbons comprising at least two layers - Google Patents

Abstract

The invention relates to the manufacture of transparent films, sheets or ribbons of plastic of excellent optical quality. It proposes a process for manufacturing these products by casting a composition suitable for casting on a flat, horizontal casting support in continuous movement in order to obtain at least one layer, which after its consolidation is detached from its support, turned over, then by casting on the face of the first layer which was initially in contact with the support during its formation of a composition in order to obtain a second layer, the first layer being placed on a casting support plan, horizontal.

Description

The present invention relates to the manufacture of films, sheets, or transparent plastic tapes, and in particular to a process in which the plastic material is fed, by casting while it is in the form of a solution, of a molten material or of a reaction mixture suitable for casting on a casting support in continuous movement relative to the casting on which the deposited layer hardens and where after hardening, the film, sheet or formed tape is detached from the casting support.

During the production, by a casting process, of transparent plastic layers having very good optical properties, the quality of the surface of the casting support is of decisive importance for the optical quality of the layers. Hitherto, in order to obtain the desired optical properties, it has been found necessary to use as casting support flat glass surfaces having the desired surface quality. We know, for example from the German patent publication DE-OS 27 26 159 a process in which the casting support is a horizontal, continuous strip of glass plates juxtaposed to each other. Also known from German patent DE-PS 24 22 543 is a process in which the casting support is a horizontal, continuous glass ribbon. that we use directly at the exit of its production line.

These known methods provide satisfactory results with regard to the optical qualities of the layers obtained. However, they also have a number of drawbacks. Thus, in the case where the pouring support is a horizontal strip formed of glass plates juxtaposed to each other, the parts of the layers which have formed above the junctions between the plates cannot be used. In the case of the use of a continuous glass ribbon, given the size of the current manufacturing units for glass, there are not always sufficient possibilities of arrangement.

The invention overcomes the disadvantages mentioned. It relates to the manufacture of sheets, films or tapes of plastic material having very good optical properties, by a casting process on a flat, horizontal support, which does not require the use of a casting support having a surface perfectly smooth, that is to say free from all the defects which could harm the optical qualities of the layers.

To this end, the invention provides a process in which a sheet with at least two layers is produced, by casting on a flat, horizontal casting support, in displacement relative to the casting, of a solution, a molten material or a reaction mixture in order to form at least a first layer which, after hardening, for example by polymerization or evaporation of solvent, is detached from the casting support, turned over, placed again on the horizontal casting support or on another flat, horizontal casting support on which it is held, and by casting on the face of this first layer, which initially was in contact with the casting support, a solution, a molten material or a reaction mixture to form a second layer having optical properties equivalent to that of the first layer. The term "inverted" means according to the invention that the face of the first layer initially oriented downward, therefore on the side opposite to the casting, is oriented upward to receive the other layer.

It is indeed remarkable, and taken advantage of by the invention, that the free face of a layer produced by a casting process is in all circumstances in the form of a flat surface with excellent optical properties, even when the casting medium does not have said optical properties to such a high degree, with con However, the first layer is after being turned over again placed on a flat, horizontal support and held on it. The invention therefore makes it possible to obtain a sheet having at least two layers, and of which neither of the two external faces, before the consolidation of the layers which gave rise to the formation of these faces, was found in direct contact with the casting support. Thus, the inevitable impression, on the face of the layer in formation which is in contact with the casting support, of undesirable surface defects of said casting support, becomes secondary: in fact, following the reversal of the first layer, the face considered constitutes an internal face covered by a second layer, also cast, of the set of layers finally produced.

It was known from Belgian patent publication 678 248 the manufacture by a solution method of a film with smooth surfaces without the use of a smooth support. To this end, it was proposed to spread a film-forming solution on the surface of a first support, to detach the film and then to spread the same solution on the surface of the film which was in contact with the support, using the film as a second support. However, this process is not suitable for the manufacture of a layer of plastic material of high optical quality, that is to say of an optical quality which meets the standards of use in laminated glazing, because this manufacture requires casting on a perfectly flat and horizontal support.

The flat and horizontal position of the first layer on the second support for the manufacture of the second layer is an essential characteristic of the invention. This position can be ensured by additional support, for example electrostatic or by suction.

We can further improve the flat and horizontal position of the first layer by stiffening it, for example with a reinforcing sheet.

The process which is the subject of the invention can be applied to the manufacture of a sheet with two layers of the same kind. In particular, the two layers can be obtained from the same reaction mixture suitable for casting and comprising the constituents necessary for obtaining an aliphatic thermosetting polyurethane, that is to say fully crosslinked. The polyol and isocyanate components required are such that at least one of the two types of components has a functionality of 3. As a component isocyanate, it is possible to use: bifunctional isocyanates such as hexamethylenediisocyanate, trimethylhexamethylenediisocyanate, 4,4'-methylenecyclohexyldiisocyanate, isophoronediisocyanate or their biurets, isocyanurates and analogous compounds tri- or plurifunctional, as well as polyols plurifunctional ie branched, for example polyesters or polyethers as they are obtained by reaction of multifunctional alcohols such as glycerol, trimethylolpropane, hexanetriol, pentaerythritol ', sorbitol, etc. with aliphatic dicarboxylic acids, such as adipic acid, or with cyclic ethers such as ethylene oxide, propylene oxide, or tetrahydrofuran. The molecular weights of the branched polyols must be from 250 to 4000 and are preferably from 450 to 2000. Such a sheet is used in particular for coating automobile windshields thanks to its highly elastic properties giving it antilaceration and d self-healing.

The process can also be applied to the manufacture of two layers of a slightly crosslinked polyurethane obtained by reactive casting at high temperature, of the order of 80 to 140 ° C., from a mixture of polyol and isocyanate components essentially. difunctional or having a small amount of either of these components in trifunctional form. In particular, the reaction mixture comprises an isocyanate component with a viscosity of less than 5000 centipedes at 40 ° C. and a polyol component, the isocyanate component comprising at least one aliphatic or cycloaliphatic diisocyanate or an isocyanate prepolymer, the polyol component comprising at least one long difunctional polyol with a molecular weight of between 500 and 4000 and at least one short diol as chain extender.

According to a variant, the method applies to the manufacture of a sheet with two layers of different nature, but having equivalent optical properties.

In particular, the first layer with a thickness for example of between 0.2 and 0.3 mm and preferably between 0.4 and 0.6 mm can be obtained from a reaction mixture suitable for casting and intended for obtaining an aliphatic thermosetting polyurethane, as defined above, and the second layer, of a thickness for example comprised between 0.01 and 0.8 mm from a solution, a melted composition or of a reaction mixture for obtaining an essentially linear thermoplastic polyurethane having adhesion properties. The starting components for the thermoplastic polyurethane can be: linear polyols such as polyesters of adipic acid having a molecular weight of 500 to 4000 and preferably from 1000 to 2000, obtained for example from 1,2-propanediol, 1 , 4-butanediol, 1,3-dimethylpropanediol, 1,6-hexane-diol, or mixtures of such linear polyesters having a molecular weight also between 500 and 4000 and preferably between 1000 and 2000, obtained from oxide ethylene, propylene oxide or tetrahydrofuran; and isocyanates such as hexamethylenediisocyanate, trimethylhexamethylenediisocyanate, m-xylylènediisocyanate, 4,4'-methylenebis (cyclohexylisocyanate), isophoronediisocyanate or their linear derivatives.

Such a sheet is intended in particular to be deposited on a transparent rigid support made of silicate glass, in order to constitute a laminated glazing in particular of an automobile windshield.

According to another variant, the first layer is always a layer of a thermosetting aliphatic polyurethane and the second layer is the slightly crosslinked polyurethane mentioned above.

The method can also be applied to a sheet with more than two layers when it is desired to obtain a multilayer sheet with good optical properties, it being understood that neither of the two faces of the sheet obtained has been placed in contact with the support. casting during their training.

According to another characteristic of the invention, one can treat the face of the first layer initially in contact with the support, before the contribution of the second layer and then protect this treatment by the contribution of the second layer. Thus, advantageously, it is possible to print the face initially in contact with the support and then cover the printing with the second layer which protects this printing. Printing can consist of the formation of filtering strips using printing ink.

The invention also relates to a device for implementing the method.

The device according to the invention comprises a flat and horizontal casting support for the formation of the first layer, means for extracting and turning the formed layer, a flat and horizontal support for the inverted layer, means for supply of the material to be poured arranged above the casting support and the the inverted layer, at least in their upstream region, and means for hardening the layers, in particular by polymerization and / or evaporation of solvent.

As described above, it is essential for obtaining good optical quality that the casting support be horizontal both for the supply of the first layer and for the support of this layer for the supply of the second layer.

The casting support for the formation of the first layer can be a horizontal endless strip. The casting support is made of a material allowing casting, for example a metal such as stainless steel. If necessary, it is coated with a separating agent facilitating the extraction of the layer formed.

The support for the inverted layer is of the same type, namely an endless, horizontal flat band.

In a preferred embodiment of the device, the casting support and the support for the inverted layer are formed from two horizontal endless metal strips, avatagely arranged one below the other, possibly covered with a layer of an agent. for separation, for example a sheet of silicone paper.

When the first layer does not have the mechanical characteristics allowing it to remain perfectly flat and horizontal on the second support, the device then comprises means ensuring this plane and horizontal maintenance. These means are for example electrostatic means. In a variant, the second support is pierced with a hole and it is associated with suction means which hold the layer pressed against it.

Other advantages and characteristics of the invention will appear in the following description of exemplary embodiments of the device in relation to FIGS. 1 and 2.

The device of Figure 1 can be used for the manufacture of a continuous sheet of plastic material with two layers, for example a layer of thermosetting polyurethane having anti-laceration and self-healing properties obtained by reactive casting of a polyol component and an isocyanate component and a polyurethane layer having adhesion properties, in particular a thermoplastic polyurethane obtained by pouring a solution.

The application which is made of this type of sheet requires it to have excellent optical properties. Like the rigid support for which it is intended, it must guarantee transparency flawless, and must therefore be completely free of streaks or any kind of surface irregularity.

This device can also be used for the manufacture of a sheet with two layers, a layer of thermosetting polyurethane having self-healing and anti-laceration properties and a layer of polyurethane having energy absorbing properties.

The lengths of the various parts which constitute it and on which the successive castings are carried out as well as the characteristics of the heating elements are adapted to the characteristics of hardening by polymerization or evaporation of solvent of the layers to be formed.

The device comprises two pouring zones, of substantially identical structure, and arranged one above the other perpendicular to a common frame 1.

The first casting zone comprises a casting head 2, for example a doctor blade casting head as described in French patent publication 2 347 170, with the aid of which the mass suitable for being deposited on a flat casting support in casting for the formation of the first layer. The mass is brought to the casting head via a conduit 3. A layer 4 of uniform thickness is deposited on the support, thanks to the casting head. The pouring support consists of a flexible and endless stainless steel tape, the surface of which is polished. This strip 6 moves thanks to the two guide rollers 7 and 8, at least one of which is driven, so that this steel strip serving as a casting support moves at constant speed in the direction of the arrow F. It slides, in the casting area, that is to say the upper part of the strip on a flat base 9 which serves as support and ensures that over the entire casting area the steel strip retains its flatness.

Above the steel strip, and following the casting head in the direction of movement of the strip, there is a frame 12, in which there are heating elements 13 enabling the layer 4 to be heated to the desired temperature. necessary for hardening, for example by sufficient polymerization of said layer to be able, later, to detach it from the steel strip.

At the level where the steel strip 6 reaches the roller 8 and reverses the direction of its movement, the hardened layer 4 (designated by 4 ′ in the figure) is detached from the steel strip and is then transported vertically downwards. When it reaches the guide roller 15, it again changes its direction of movement and finds a horizontal direction of travel, in the direction of the arrow F '. It advances, in this direction, on a steel strip 16; the face which, in the first casting zone, was not in contact with the steel strip, is now in direct contact with it. The steel strip 16 is similar to the strip 6. It travels by means of two guide rollers 17 and 18, at least one of which is driven, at the same speed as the strip 6, and, in its upper part, in an opposite direction indicated by arrow F '. In the same way as above, the ribbon slides, in its upper part, on a flat base 19 which serves as a support for the layer 4 ′, and thus ensures that the steel ribbon retains its flatness throughout the area where it supports the layer, or layers.

At the entrance to this second casting zone, above the steel strip 16, is a second casting head 22, of the same type as the first, into which is brought a mass suitable for casting by the conduit 23. Thanks to this casting head, a second layer 24 of uniform thickness is deposited on layer 4 '.

Above the steel strip, and following the casting head, in the direction of movement of the strip, is a frame 26 comprising heating elements 27. They allow the maintenance of a regulated temperature, in order to accelerate the drying of freshly deposited layer 24. The pipes 28 make it possible to aspirate any solvent vapors. At the end of the steel tape transport zone 16, the layer 24 is perfectly dried and solidified, so that the sheet 30, composed of the two layers 24 and 4 ′ deposited according to the process indicated, can be at this level detached from the ribbon; one can for example transport it vertically upwards, after having changed its direction at the level where the steel strip reaches the guide pulley 17, then wind it on the roller 34 after having disengaged it from the casting support thanks to the rollers 32 and 33.

FIG. 2 represents a device for manufacturing a three-layer sheet 35 comprising an internal impression obtained by depositing an ink on the first layer. This device comprises a first pouring zone equipped with a pouring head 36 disposed above the upstream part of a pouring support constituted by an endless stainless steel strip 37, driven by two rollers 38, 39. This tape slides on a flat base 40 which serves as a flat, horizontal support. Downstream of the casting head, arranged under the tape metallic, heating elements 41 ensure the polymerization of the layer 42. Cleaning means 43 are provided on the return of the steel strip. Arranged downstream of the first casting zone, the device comprises a printing system with a printing roller 44, a counter roller 45, and a tank 46 containing the printing ink 47. The printing is applied by the roller 43 on the face 48 which was in contact with the metallic strip.

The printing can be of different types: it can be for example filter bands. The printing ink is dried by heating elements 49. After passing around the rollers 50, 51, the printed layer 41 arrives at a second casting zone where it is placed on an endless metallic ribbon 52 driven by two rollers 53 , 54. The tape slides on a horizontal and flat table 55. The metal tape and the table are drilled with holes so that a suction system 56 makes it possible to apply the layer perfectly on the metal tape. A second layer 57 is deposited on the first layer by means of a casting head 58. Heating elements 59 ensure the polymerization of this second layer which covers the impression previously deposited on the layer 41.

A third casting zone, arranged in the downstream part of the same metal strip 52, allows the addition by a third casting head 60 of an additional layer 61, for example an adhesive layer which is then hardened by the heating elements 62. After detaching the three-layer sheet 35 from the metal strip 52, the sheet is wound up to form a roll 63 after it has been coated on its two faces with protective films 64 and 65 cut by the rollers 66 and 67.

EXAMPLE 1

Using the device described in relation to FIG. 1, a two-layer sheet is produced, namely a layer of thermosetting polyurethane and a layer of thermoplastic polyurethane having adhesion properties.

• On mélange de façon homogène, en évitant la formation de bulles d'air par dégazage sous vide: -
  • - 1000 g d'un polyéther préparé par condensation d'oxyde de propylène avec un triol, avec un poids moléculaire d'environ 450 et une teneur en radicaux OH libres de 10,5 à 12 %,
  • - 23 g de 2,6-di-t-butyl-p-crésol,
  • - 0,5 g de dilaurate de dibutylétain, et
  • - 1000 g d'un Muret de 1,6-hexaméthylènediisocyanate ayant une teneur en radicaux NCO libres de 21 à 25 %.

A composition is prepared which is suitable for casting for the manufacture of the thermosetting polyurethane layer as follows:

• One mixes homogeneously, avoiding the formation of air bubbles by degassing under vacuum: -
  • - 1000 g of a polyether prepared by condensation of propylene oxide with a triol, with a molecular weight of approx. ron 450 and a content of free OH radicals of 10.5 to 12%,
  • - 23 g of 2,6-di-t-butyl-p-cresol,
  • - 0.5 g of dibutyltin dilaurate, and
  • - 1000 g of a low wall of 1,6-hexamethylenediisocyanate having a content of free NCO radicals of 21 to 25%.

A composition suitable for casting is prepared for the formation of the adhesive layer as follows:

• - de 1000 g d'un polyester linéaire issu de 100 parties d'acide adipique et de 56 parties d'hexanediol-1,6, de 30 parties de 2,2-diméthylpropanediol-1,3, et de 7 parties de propanediol-1,2, ayant un poids moléculaire de 1850 et une teneur en radicaux OH libres de 1,5 à 1,6 % et,
• - de 128 g de 4,4'-méthylènebis (cyclohexylisocyanate) ayant une teneur en radicaux NCO libres de 31,5 %.

Polyaddition is carried out in a reaction tank, by heating:

• - 1000 g of a linear polyester from 100 parts of adipic acid and 56 parts of 1,6-hexanediol, 30 parts of 2,2-dimethylpropanediol-1,3, and 7 parts of propanediol- 1.2, having a molecular weight of 1850 and a content of free OH radicals of 1.5 to 1.6% and,
• - 128 g of 4,4'-methylenebis (cyclohexylisocyanate) having a content of free NCO radicals of 31.5%.

The cooled melt is granulated and dissolved in dimethylformamide to obtain a 10% solution.

From these compositions suitable for casting, a sheet composed of two layers is produced using the casting device as follows:

The reaction mixture is poured onto the endless belt 6 coated with a separating agent as described in French patent publication 2 383 000 using the casting head 2 to form a layer 4 which, under the action of the heating elements 13, hardens by polymerization to give the layer 4 '. At the end of the strip 6, after passing around the roll 8, the layer 4 ′ is detached from the support, and placed on the tape 16 after passing around the roll 15. The solution of thermoplastic polyurethane is poured onto the layer 4 using the casting head 22. Under the action of the heating elements 27, the solvent is evaporated, the vapors being sucked into the pipes 22, and the casting layer 24 hardens. The two-layer sheet is extracted from the ribbon 16 and after passing around the rollers 31, 32, 33 is wound on the roll 34.

EXAMPLE 2

Using the device described in connection with FIG. 1, a transparent double-layer plastic sheet is produced, namely an adhesive layer having energy-absorbing properties and a transparent coating layer of plastic material. resistant to scratching and abrasion designated by self-healing layer or internal protective layer, because oriented towards the interior of the passenger compartment in the case of a windshield.

• - 1000 g d'un polyéther d'un poids moléculaire d'environ 450 obtenu par condensation d'oxyde de 1,2-propylène avec du 2,2-bis (hydroxyméthyl-1-butanol) et ayant une teneur en radicaux hydroxyle libre d'environ 10,5 à 12 % contenant 1 % en poids d'un stabilisant, 0,05 % en poids d'un catalyseur à savoir du dilaurate de dibutylétain, 0,1 % en poids d'un agent nappant.
• - 1020 g d'un biuret de 1,6-hexanediisocyanate ayant une teneur en radicaux isocyanates libres d'environ 23,2 %.

On the casting support 6, a homogeneous mixture is poured in the following proportions of:

• - 1000 g of a polyether with a molecular weight of about 450 obtained by condensation of 1,2-propylene oxide with 2,2-bis (hydroxymethyl-1-butanol) and having a content of free hydroxyl radicals from about 10.5 to 12% containing 1% by weight of a stabilizer, 0.05% by weight of a catalyst, namely dibutyltin dilaurate, 0.1% by weight of a coating agent.
• - 1020 g of a 1,6-hexanediisocyanate biuret having a content of free isocyanate radicals of approximately 23.2%.

A uniform layer is formed which, after polymerization under the effect of heat, for example about 15 minutes at 120 ° C., has a thickness of about 0.19 mm and self-healing properties. After extracting the layer of the ribbon 6, it is placed on the ribbon 16 for the casting of the so-called layer.

To manufacture the layer having energy absorbing properties, the polyol component is prepared beforehand by mixing a polytetramethylene glycol of molecular mass 1000 (for example the product sold under the name Polymeg 1000 by the company QUAKER OATS), with 1,4-butanediol, the proportions of the two constituents being such that polytetramethylene glycol provides 0.37 equivalent in hydroxyl groups while 1,4-butanediol provides 0.63.

The polyol component incorporates a stabilizer at a rate of 0.5% by weight of the total mass of the polyol component and the isocyanate component, a coating agent at a rate of 0.05% by weight calculated in the same way and a catalyst namely dibutyltin dilaurate in an amount of 0.02% by weight calculated in the same way as above.

The isocyanate component used is 3-isocyanatomethyl-3,5,5 -trimethylcyclohexylisocyanate (IPDI) having urea functions obtained by partial hydrolysis of IPDI and having a content of NCO groups of approximately 31.5% by weight.

The components are taken in quantities such that the NCO / OH ratio is 1.

After degassing the components under vacuum, the mixture brought to about 40 ° C. is poured onto the layer of self-healing polyurethane. previously formed and which has been placed on the ribbon 16. A layer of approximately 0.53 mm thick is thus formed which is subjected to a polymerization cycle consisting of 25 minutes of heating to approximately 120 ° C.

The two-layer sheet is then removed from the support 16 and it can be easily handled, stored or used immediately afterwards for the manufacture of laminated glazing.

EXAMPLE 3

For the manufacture of the two-layer sheet of Example 2, it is also possible to envisage first forming the layer having energy-absorbing properties, and then, after its extraction from the casting support and its inversion, to form the layer having adhesion properties.

Claims (19)

1. A method of manufacturing transparent films, sheets or ribbons of high optical quality in plastic material with at least two layers, characterized in that it flows on a flat and horizontal casting support, in relative displacement relative to the casting, a solution, a molten material or a reaction mixture in order to form at least a first layer which, after hardening by polymerization or evaporation of solvent for example, is detached from the casting support, turned upside down, again placed on a flat casting support and horizontal, then a solution, a molten material or a reaction mixture is poured onto the face of this first layer which initially was in contact with the casting support in order to form a second layer having optical properties equivalent to those of the first layer. 2. Method according to claim 1, characterized in that the first layer formed and that deposited after hardening and inversion of the first are obtained from the same composition suitable for casting. 3. Method according to claim 2, characterized in that said composition comprises the constituents necessary for obtaining an aliphatic thermosetting polyurethane. 4. Method according to claim 1, characterized in that the first layer formed and that deposited after consolidation and inversion of the first are obtained from different compositions. 5. Method according to claim 4, characterized in that one of the layers is obtained from a reaction mixture comprising the constituents necessary for obtaining a thermosetting aliphatic polyurethane and the other layer from a solution, of a molten composition or of a reaction mixture of a thermoplastic polyurethane, essentially linear. 6. Method according to claim 4, characterized in that one of the layers is a layer of thermosetting aliphatic polyurethane and the other is a layer of a slightly crosslinked polyurethane, obtained by reactive casting of a mixture of polyol components and isocyanates exclusively difunctional or having a small amount of one or the other of these components in trifunctional form. 7. Method according to one of claims 1 to 6, characterized in what is treated on the face of the first layer, initially in contact with the support, before the addition of the second layer which covers the treatment. 8. Method according to claim 7, characterized in that one prints the face of the first layer. 9. Device for implementing the method according to one of claims 1 to 8, characterized in that it comprises a flat and horizontal casting support for the formation of the first layer, extraction and turning means of the fabricated layer, a flat and horizontal support for the inverted layer, means for supplying the material to be poured arranged above the casting support and of the support for the inverted layer, at least in their upstream zone, means for curing layers by polymerization and / or for solvent evaporation. 10. Device according to claim 9, characterized in that the casting support is a horizontal endless conveyor belt. 11. Device according to claim 10, characterized in that the conveyor belt is a metal band, in particular a steel tape. 12. Device according to claim 11, characterized in that it comprises a casting support formed of an endless horizontal and flat conveyor belt of steel 6 and a support for the inverted layer also formed of a horizontal, planar conveyor belt , endless steel 16, the two bands being placed one above the other, a drive system 15 for extracting and turning the first layer formed, scraper casting heads 22 and 2 for the contribution of the material to be poured and of the heating elements 13 and 27 allowing the hardening of the layers formed. 13. Device according to one of claims 9 to 12, characterized in that the casting support is covered with a separating agent. 14. Device according to one of claims 9 to 13, characterized in that the means for supplying the material to be cast are scraper casting heads. 15. Device according to one of claims 9 to 14, characterized in that it comprises means for treating opposite the first layer which was initially in contact with the support. 16. Device according to claim 15, characterized in that the means for processing are printing means. 17. Device according to one of claims 9 to 16, characterized in that it comprises means for maintaining the first layer on the casting support for the manufacture of the second layer. 18. Device according to claim 17, characterized in that the means for maintaining the first layer are suction means associated with a casting support pierced with holes. 19. Sheet of high optical quality obtained by implementing the method according to one of claims 1 to 8.

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